Ultra short wave oscillator



C. w; HANsELl.

ULTRA SHORT WAVE'OSCILLATOR Filed July 25, 1941 June' i8, i946.

lNvENToR Wha/ABZ@ BY Z WW ATTORNEY Patented June 18, 1946 fiom-TEDSTATES *PATENT lOFiFfl-CFE' K 2,402,397 vlurfrimf SHORT WAVE oscmm'roa`Clarence WmHansell, Port-Jeuersony- Y.,as signor to RadioCorporationof.America,=a.cor

poration vof A.Delaware Application-"-Jilly'li 19441, Serial No.`l403,985

, Claims.

.This'invention relatesftdelectronzdischargegdevicelapparatusg-and'moreparticu'larly toa-masnetron oscillator: fori :the-generation; ofzultra high fre quency: waves.

An object ofrthef.present.iinventionris toprovide an electron dischargedevice oscillator having a completely enclosed anode circuit formed by aplurality of physically spaced anode seg- -ments'whovse"circi1ri'1ferential` length-has a' particular `relation i-to'the 'frequencyfof I operation.

Anther- 'object f Tthefpresent invention isto provide` a splitanodeIoscillator :wherein the width ofthe gaps between theadjacentanode'fisegments and"the' natural` period" of lcircumierentialLoscillation of v'the anode structure," taken together with '1 themagnetic "eld and #potential adjustments,

control the frequency 'of oscillations.

`It hasl been customary' -in thepastfto employ magnetron oscillators ofthe split anode\type Whereinthe Ianode-'segments 'operate inpushpullrelation to each other. "'Insuch'fknown mag- `netron'oscillators,v each`anode-l segment =has for its entire circumferential --length 'one-instantaneous potential,A andthe normal '-mo'de of loscillation isvgovernedbytheeconstants of the-fex ternal tuned'circuits' andthefadjustmentsfof the magnetic field, as Well as by the-anodeivoltage.

vlin these oscillators; the circumferential length of the anode-segmentsbears no especial relation to the wavelength or 'frequency 'of'operation. 'iThe f improved; magnetron oscillator of `the presentinvention, however,"employsfa v5new mdef-*oscillation which obviateslthe 'need'orexternal tuned circuits for the anode' structure. lf-Byconstructing the 'anode segments of my improved oscillator sol that theIcircumferential length thereof bears 1a desired relation tothewavelength or frequency of operation, I amiablefto obtain oscillationsina" circumferential *direction around the anode structure. In theoscillator ofthe inventiomthe circumferential 'length ofeach anode'segment isv electrically' one-half Wavelength'A -for 'one'4 mode ofoscillation, or multiples of one-half wavelength off'other modesof""os`cilla'tion. "The Icircumferential 'portions ofv'ftl-iefandefsegmentsftl'ius ldefine inductancesfwhile the'` gaps"between-@thei'ande segments form capacitances "which Vtogether-provide fa" primary influence' upon thefrequency of oscillations. 'Asecondary'ini'luence ini determining the"'frequency"f oscillations ofmyfoscill'ator is the' V'electron-1velocity irrithe'region of thefgapsy@which is dependent upon'thev anode 1 potential re1- lativetothecathodeionfilament o .-By'V employing1fcircumferentialfroscillationsthe u oscillatorzrof` the-inventionprovidessa veryzwide f .sociated X kconnecting leads.

1o off. operation than invknown types ofrmagnetron .oscillators lwhichdo. not employ circumferential oscillations.

' One:4 advantage i ofthe. osc'zillatorv of/therfinvention-liesin-lthe'l' fact 'that it.:is:possiblet-to obtain l. oscillations by'virtue'. ofeelectron travel over-:dis-

tances .Which arewquiteshorttcompared: toi-the wavelengths`soL-.thatfvthe.electron velocitiesiand anode :Voltage: required: for a,given --wavelength may Yjbe yvery; muchfless thany 'inother .ty-pes; of

oscillators.

.'Avfeature of. the A`invention residesxin the: fact 4 that :the:`electrons :circle "the: Yfilament in one .direction'v only, and; impingeupon onlyv oney endxof each anode segment. vAnother feature lies 4inathe*use-of means.-emp1oyed for preventing-.electrons Yemanating. fromthelament. or cathode .fromidisjfpersing inwrong directions. In .thisway; I; am .able-toreducef emission of those electronswwhich do not'-aid': in producing vcircumferential oscil- A latOIlS.

- A' more detailed 'description fof: the invention lfollows Vinconjunctionwith-1: a .'drawing, wherein: ,-Fig.A lfshoWsv incrosssectiona view,` oi". the essential-4 features A of 'f a split-r anodemagnetron-os- 35 cillation,A generator of the invention,` the. arrowsdiagrammatically; representing the; paths vtaken .by J'the l.electronsunder different conditionsrzof operation;

.2.schematically, shows 'the embodiment: of

40 Fig. 1 in a-.completecircuitr arrangement;

Fig.y 3 is f a detail showing an' alternative Iform offilament orIcathode for :preventing electrons from Vdispersing` inrfwrongdirections;

vFigli ist amodication ofthe oscillatonof'Fig.

.1- showing how l more than twof anodeasegments can-be employed-in` ananode structure and Fig.- 5 .is aview in crosssection. of- -theoscillator of: theinvention provided withA .a preferred f form ofanodeconstruction.

The oscillation generator shown-in Fig; loom- 'prisesanfevacuatedenvelope l made of: anysuitf 1 ablefmaterial'suchfasf glass, VcontainingEwithin it azcentrally located linear kelectron "emitting cath- 'ode 2,:andian:.anodeistructurel composed of Ia pair of spaced or split anodesegments 3A Saeach 3 of which has a circumferential dimension which iselectrically one-half wavelength long for the lowest mode ofoscillation. These anode segments may be a multiple of a half Wavelengthlong in a circumferential direction for other modes of oscillation. Therelation of the circumferential dimension of each anode segment to theWavelength is indicated in the drawing. A eld coil 4, which may or maynot employ iron to aid its effect, surrounds the envelope and functionsto produce an intense but constant magnetic eld which has flux linesrunningthrough the envelope in a direction parallel to the cathode 2 soas to influence the movement of the electrons emanating therefrom. Gridwires 5, 5 serve to reduce electron emission from the cathode 2 in thosedirections which do not aid in the produc- These grid tion ofcircumferential oscillations. wires are maintained at near zero ornegative potential relative to the cathode 2. Both anode segments 3, 3are of equal length and are maintained at rthe same positive directcurrent poten- Y tial relative to the cathode;

As is Well known, the electrons which ordinarily tend to move in radiallines from the cathode, when subjected to the action of a magnetic eldfrom coil 4 in a direction parallel to the cathode, or at right anglesto the electric field between the electrodes and to the paths of theelectrons, will tend to move in a spiral line tangentially to the anodeVas indicated by the arrows of arcuate paths X and Y. As the strength ofthe magnetic field is increased, these spiral lines contract toward thecathode, and if the field is made strong enough, it will be apparentthat substantially none of the electrons will reach the anode segments.If the strength of the magnetic eld is decreased, however, substantiallyall of the electrons can be made to reach the anode. In the presentinvention, the field strength and the value of the positive directcurrent potential applied to the anode segments 3, 3 are adjusted to acritical value so that the electrons just skim past the ends of theanode segments and follow either the path X or the path Y, dependingupon the instantaneous potential of the ends of the anode segments. Theelectrons, it should be noted, will strike or come close to a negativeanode end A or D when the adjacent ends C or B have a potentialmomentarily in excess of the positive applied direct current potential;a posteriori, the electrons will not reach or come soclose to ends A andD when the adjacent ends C and B are less positive than the applieddirect current potential. It will be evident that the potentialuctuations of the anode edges A and C, and B and D control the paths ofelectron motion. Since points A and C, and B and D have a potential 180out of phase,'and the two anode segments are electrically closelycoupled together, we thus have conditions which can maintainoscillation.

In the production of oscillations, high fre quency fluctuations inpotential between adjacent ends of the anodes cause :fluctuations inpaths taken by the electrons in a manner to increase the potentialfluctuations up to a limiting value. Many electrons strike on or nearportions A and D but a large number of the electrons ily in the curvedpath X and return to the cathode. The oscillating currents in the anodesgive lrise to fluctuating or oscillating magnetic eld strengths in thespace between cathode and anodes 'and this also may contribute to thecontrol of electron paths and aid in the production of oscilla tions. j

It should be noted that the electrons circle the cathode 2 in onedirection only and hence there is only one end of each anode segment Aor D upon which the electrons impinge. Since anode segments 3, 3 areeach a half wavelength long electrically, or a multiple thereof,depending upon the mode of oscillation employed in the operation of thedevice, there will be a. wave propagated around the anode structurewhose resonant period is determined in part by the circumferentialdimensions of the anode segments and the spacings therebetween, and inpart by the electron velocity in the region of the gaps between theanode segments, in turn dependent upon the anode potential relative tothe cathode. Assume, by way of example, that the distance betweenadjacent edges of the anodes is 0.25

centimeter, then the portion of electron path most active in producingoscillations may be on the order of 1 centimeter. The anode potential,which may be applied in short pulses, may be 25,000 volts, correspondingto electron velocities of 9 109 centimeters per second. The timerequired for each electron to pass through the 1 centimeter activeregion will then be second. If this time is allowed to be no greaterthan say 0.1 of thetime of one cycle of oscillation, then the frequencyof oscillation will be 900 megacycles. For thecase assumed, this wouldlikely be the frequency at which transit time effects begin to reducethe efficiency and strength of oscillation as the frequency is increasedbut it is not the highest frequency for which oscillations may beproduced for this mode of oscillation, when the anodes are properlydimension for resonance.

Other higher frequency modes of oscillation are obtainable correspondingto elfective time delays of 1, 2, 3, 4, etc., cycles of oscillation forelectrons to pass through the active space between ends of the anodes.Thus, there is a series of modes of oscillation obtainable according tophysical dimensions and intensity of electric and magnetic fields.

Fig.2 illustrates how the oscillator of Fig. 1 can be embodied in acomplete circuit arrangement. It should be noted that anode segments 3,3 are of equal length and have equal circumferential dimensions. Inorder to supply the anode segments with a positive direct currentpolarizing potential relative to the cathode, there are provided quarterwavelength leads 6, 6 which join the ends of the anode segments to thepositive terminal of battery 1 through radio frequency choke coils 8, 8.The lengths of the leads 6 are such that there is provided a highimpedance at the points thereof joining the anode segments for energy ofthe operating frequency. A radio frequency by-pass condenser 9 bridgesthe ends of leads 6, 6 at the location nearest the choke coils 8, 8. Forderiving output energy from the oscillator, there may be provided a loopI0 which can couple inductively with the leads 6, 6 at a suit able pointintermediate its ends. Obviously, output energy may be obtained not onlyby the output coupling loop I0 but* also by electromagnetically couplinga loop or open-ended con-` densers to one or both of the anode segments3, 3. Further, the nature of the oscillator is such that it can radiateenergy directly, for which reason it can, if desired,fbe mounted infront of a reector to provide directivity of radiation. It

fag-rogge? trcmagnetically shielded.

odeisf coated with electroni emissive'v material at f twoA points l i, Hinfo-r'der -to preventelectronsv f-rornl-dispersing in thelwrong.ldirections. Obviously; if f fthecathode of Fig oscillator of Ytheraven-ums?.therewilll `be nef-need f for employing grid wires 5; 5.A Y

Fig.fl4 shows, 'informs-section, an oscillationA generator which `is amodification-of the-'oscillator offiFig.' 1, differing therefrom;mainlylinl-the-use' of ani-additional' i anode-segment. ''It will? thusbe evident' that' the anode-segments are `*not `limited td two, as-shownFigbbut may be increased in number to three, as shown in Fig. 4, or anydesired number provided the desired relation of circumferential lengthand resonance frequency to wavelength of operation is followed. Itshould be noted in Fig. 4 that here again the electrons.. circle thefilament in one direction only. To reduce electron emission from thecathode in undesired directions, there are now employed in Fig. 4 threegrid wires 5', 5 which are maintained at zero or negative potentialrelative to the cathode. If desired, a cathode similar to that shown inFig. 3 may be employed in Fig. 4 with the modi-f cation that the cathodebe coated at three equally spaced points circumferentially thereof, inorder to furnish electron emission at the desired locations, in whichcase it will not be necessary to employ the grid wire 5', 5.

Since, for `the type of operation described, electrons impingeprincipally on or near one edge f each anode segment, this edge willhave greatest..

heating. As an aid to disposing of this heat, and to lengthen the anodelife when very high potentials are used, I contemplate increasing thethickness of metal at and near this edge after the manner described inmy United States Patent No. 2,037,977. Fig. shows a fragmentary View ofan oscillator of the invention with the' anode segments of greater massat the portions predominantly struck by the electrons.

What is claimed is:

l. Electron discharge apparatus comprising a linear cathode, aself-contained oscillatory circuit comprising a plurality of spacedanode segments surrounding said cathode, the circumferential length ofeach of said anode segments being electrically one-half wavelength forthe lowest mode of oscillation and said circumferential portions deninginductances, the spaced portions of said anode segments formingcapacitances in circuit with said inductances.

2. An electron discharge device oscillator comprising a linear cathode,a self-contained oscillatory circuit comprising a plurality 0f spacedanode segments of equal circumferential length surrounding said cathode,the circumferential length of each of said anode segments beingelectrically a multiple, including unity, of one-half wavelength for amode of oscillation and said circumferential portions defininginductances, the spaced portions of said anode segments formingcapacitances in circuit with said inductances, whereby there areObtained oscillations in a circumferential direction around said anodesegments.

3. An electron discharge device oscillator comprising a linear cathode,a plurality of spaced anode segments surrounding said cathode, the

circumferentmnengths.:en said :anode segments l prising a'ilinearcathode, vva plurality vf spaced i'ande iksegments surrounding f saidcathode, the l circu'niferen'tial"v lengths' :off 'said' `,anodesegments having "flux ilinesf'finl adirectionllparallel to f saidcathode, '-the circumferential 'portions-of said anode segments deninginductances,-the spaced l"portions :fsaid anodesegments formingcapacitancesin circuit withsaid inductances,. v

l 4; An y"electron discharge' device oscillator' combeing a multiple;including-unity, of' a half-wavelength long 'fora/'desired 'mode of'.oscillation,

'-nieans -forprodu'cingea'l constant magnetic i field "cathOde, lthe fcircumferential lportions '#cf'fsaid tive to said cathode forcontrolling the electron emission distribution in said oscillator.

5. An electron discharge device oscillator comprising a linear cathode,a plurality of spaced anode segments surrounding said cathode, thecircumferential lengths of said anode segments being a multiple,-including unity, of a half wavelength long for a desired mode ofoscillation, means for producing a constant magnetic eld having fluxlines in a direction parallel to said cathode, whereby the electronsemitted from saidcathode circle the cathode in one direction, thecircumferential portions of said anode segments defining inductances,the spaced portions of said anode segments forming capacitances incircuit with said inductances in virtue of which electrons impingesubstantially solely on one edge of each anode segment to produceoscillations in a circumferential direction around the anode segments,said one edge of each anode segment being thicker than the otherportions thereof to hasten heat dissipation.

6. An electron discharge device oscillator comprising linear electronemitting means, a selfcontained oscillatory circuit comprising aplurality of spaced arcuate anode segments surrounding said electronemitting means, said means comprising a plurality of coats of electronemission material of the same number as the number of anode segments,said coats being parallel and symmetrically arranged relative to oneanother in such manner as to prevent electron dispersion in undesireddirections, the circumferential length of each of said anode segmentsbeing electrically a multiple, including unity, of one-half wavelengthfor a mode of oscillation, said circumferential portions defininginductances, the spaced portions of said anode segments formingcapacitances in circuit with said inductances.

7. An electron discharge device magnetron oscillator comprising a linearcathode, a self-contained oscillatory circuit comprising a plurality ofspaced anode segments surrounding said cathode, means for producing aconstant magnetic field having flux lines in a direction parallel tosaid cathode, whereby the electrons emitted froml said cathode circlethe cathode in one direction, the circumferential lengths of said anodesegments being a multiple, including unity, of a half wave-length longfor a desired mode of oscillation, and grid Wires of the same number asthe number of said anode segments arranged parallel and symmetricallyaround said cathode for direction parallel to said electron emittingmeans,v

the circumferential portions of said anode ,seg-i ments deninginductances, the spaced portions of said anode segments formingcapacitances in circuit with said inductances, and means for con- 8trolling the electron emitting distribution in said oscillator toprevent"4v dispersion of electrons in undesired directions.

9. An oscillator in accordance with claim 7, in

cluding means for maintaining said anode segments at a positivepotential and said grid wires at a negative potential relative to saidcathode.

10. Electron discharge apparatus comprising a linear cathode, aself-contained oscillatory circuit comprising a plurality o1' spacedanode segments surrounding` said cathode, the circumferential lengths ofsaid anode segments being a multiple, including unity, of a halfwave-length long for a desired mode of oscillation and saidcircumferential portions dening inductances, the spaced portions of saidanode segments forming capacitances in circuit with said inductances,.

CLARENCE W. HANSELL.

